Images: Marko Freese & Leander Höhne ©
Conservation measures for the European Eel aim to ensure escapement of a sufficient number of mature eels from each river system to the sea. As quantitative surveys are complex and not always feasible, the evaluation of management goals is often based on population models. However, results of these modelling approaches usually are subject to great uncertainties. The BALANCE project combines a “mark-recapture” study approach and acoustic telemetry in order to get a robust quantification of the actual silver eel escapement. The use of acoustic telemetry enables us to separate eels that start or continue their seaward migration after tagging from those that stay resident in the system before migrating at a later stage. The actual silver eel escapement is then estimated from the proportion of migrating, individually marked fish in the total catch of a fishing gear. Empirical results will be compared to predictions from the German model-in-use to project silver eel escapement for model validation and identification of refinement potential.
Acoustic receiver stations along the river provide insights into the migratory behaviour depending on the degree of maturation of the silver eels and allow the identification of local migration obstacles (e.g., through navigation locks). Moreover, the influence of environmental parameters (e.g., temperature, moon phase and river discharge) on the migratory behaviour will be analysed to enable predictions of the timing and magnitude of eel migration using environmental data.
Contact person: Leander Höhne